1. Technical Field of the Invention
This invention relates to telecommunication systems and, more particularly, to a method of implementing a private charge rate in a cellular radio telecommunications network.
2. Description of Related Art
Multi-level layered cellular radio architectures are known in the art and are utilized to increase capacity in the cellular network, especially in densely populated urban areas. In these hierarchical networks, microcells and picocells share capacity in areas also covered by larger macrocells. Server selection and handoff decisions can be quite complex in these networks, and U.S. Pat. Nos. 5,499,386 and 5,640,677 to Karlsson disclose a method of best server selection in which a decision as to the best serving cell for a mobile station is made based upon a preference value assigned to each cell and the signal strength with the mobile station. Microcells and picocells are preferred in this method since they add capacity to the network. For purposes of this disclosure, the term "microcell" is construed as including picocells as well.
In an office building, the owner may install a private wireless office system which may include a plurality of microcells providing cellular coverage for private subscribers within the office building. Nearby, there may be a base station for a macrocell which provides public coverage of an area which includes the office building. Signals from outside the office building (for example, from the nearby macrocell base station) penetrate the building, and it is possible for a MS within the building to access the Public Land Mobile Network (PLMN) through the macrocell. MSs that belong to the private system are programmed with a private system identification number that links them to the private system. Therefore, when the MSs attempt to access wireless service from within the building, they automatically select one of the microcells within the private system. The difference from the regular hierarchical cell structure described by Karlsson is that the private microcell is preferred only for the subscribers of that private system.
Typically, the owner of the private system may pay a monthly flat fee to the public operator for system access, or may pay a preferential rate known as a private charge rate. Following a call by a private subscriber, the mobile station identity (MSID) as well as the identity of the private cell (CELLID) is placed in the charging record to ensure that the call is billed at the preferential rate. Additionally, if only a portion of the call is conducted in the private cell, then that portion of the call is billed at the preferential rate, and the remaining portion is billed at the public rate. For purposes of this disclosure, reference to a call placed in a private cell also refers to the portion of the call conducted in a MS's private cell when the call spans several cells, one of with is the MS's private cell.
If the private system fUils, the private subscriber's calls are handled by the public system rather than the private system. If so, the subscriber may think his calls are free, or at the preferential rate, when they are not. MSs that belong to the private system typically provide an indication to the subscriber of whether the MS is operating on the private system or the public system. However, the subscriber may not notice which system is indicated, and may continue to place and receive calls. Even if the subscriber notices the indication that the MS is operating on the public system, the subscriber's only choices are to pay the higher public rate, or delay his calls until the private system is operating again. Private cellular systems may have less capable operation and maintenance (O&M) systems and less redundancy than the public system, and therefore may take longer to repair when they fail. Thus, this situation can be a major problem for private subscribers.
There are no known prior art teachings of a solution to the aforementioned deficiency and shortcoming such as that disclosed herein. The prior art describes how to implement a private system, but does not teach or suggest a method of charging for the calls which overcomes the above problem. In particular, PCT Patent Application WO 97/34437 to Widegren discloses a system allowing roaming between a wireless office system and the PLMN. However, Widegren does not teach or suggest a method of charging for calls in which a private subscriber can avoid being charged a higher public rate when the private system fails.